1. Field of the Invention
The present invention relates to a fusing and fixing unit of an image forming apparatus, and more particularly, to a fusing and fixing unit of an image forming apparatus which is improved so as to increase the temperature of a fusing roller within a fast time and reduce a warm-up period.
2. Description of the Related Art
An image forming apparatus, in particular, an electrophotographic image forming apparatus, generally forms a toner image on a paper on which an image will be printed, through a process of charging a photoreceptor with a predetermined potential, scanning light onto the photoreceptor, developing a latent electrostatic image into a toner image, and transferring the toner image. Since the toner image is put on the paper, the image forming apparatus applies heat and pressure to fuse and fix the toner image to the paper. Here, fusing and fixing refer to an operation of applying heat and pressure to the toner image which is formed on a print medium, e.g., the paper, so as to fuse the toner image with heat and fix the toner image to the paper with pressure.
To save energy and prevent the internal temperature of the image forming apparatus from increasing, the image forming apparatus manages the surface temperature of the fusing roller during a printing operation through several temperature stages, e.g., warm-up, stand-by, printing, and sleep (power save) fusing temperatures.
The warm-up period refers to a period from when power is first turned on or from a sleep (power save) mode to a stand-by temperature, and the surface temperature of the fusing roller during the warm-up period is the warm-up temperature.
The stand-by fusing temperature state refers to the lowest temperature, which can increase up to the printing fusing temperature so that the image forming apparatus supplies a printing paper and prints an image on the printing paper through an electrophotographic process at the maximum printing speed.
The printing fusing temperature state refers to a fusing temperature needed to fuse and fix the toner image to the paper so that the toner image stably sticks to the paper after the printing operation.
The sleep (power save) fusing temperature state refers to a period in which a fusing temperature is maintained at room temperature by intercepting power from being applied to a heat source to save power-related energy when the printing operation is not performed for a long period of time.
Accordingly, the warm-up period is important to the image forming apparatus.
A conventional fusing and fixing unit uses a halogen lamp as a heat source to heat the surface of the fusing roller to a temperature required to instantaneously fuse the toner image, passes the paper to which the toner image is formed between the fusing roller and a pressing roller, and fixes the fused toner image to the paper.
After the fusing roller is heated to the printing fusing temperature state by heat generated by the halogen lamp, which is installed in the center of the fusing roller, the toner image is fused and fixed to the paper when the paper passes between the fusing roller and the pressing roller.
The halogen lamp uses a radiant heating method by which the inner surface of the fusing roller, which is spaced apart (generally 5-20 mm) from the halogen lamp, is heated through an air gap (between the halogen lamp and the inner surface of the fusing roller). However, since the halogen lamp has poor heat radiation efficiency, it takes a considerable amount of time to heat the inner surface of the fusing roller. As known in the art, if the halogen lamp is used as a heat source, the warm-up period requires 30 seconds—1 minute in a single color image forming apparatus but 3-5 minutes in a multi-color image forming apparatus.